Retaliation or discrimination, in any manner, against any person who has opposed any activity prohibited by the provisions of sections 20-132 to 20-143 or who has testified, assisted, or participated in any manner in any investigation, proceeding, or hearing conducted pursuant to sections 20-132 to 20-143 shall be discriminatory practice and shall be punishable according to the provisions of sections 20-132 to 20-143.